Communication device, communication control method and communication system

ABSTRACT

There is provided a communication device including: a first radio communication unit capable of radio communication in accordance with a first communication method; and a second radio communication unit capable of radio communication in accordance with a second communication method using a higher frequency band than the first communication method, wherein the first radio communication unit transmits an instruction signal instructing to learn a beam directionality to another communication device, and the second radio communication unit transmits a beam reference signal used for learning a beam directionality to said another communication device after completion of transmission of the instruction signal by the first radio communication unit and before reception of a response signal to the instruction signal.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a communication device, a communicationcontrol method and a communication system.

2. Description of the Related Art

A new communication method for enhancing the communication speed ofradio communication with use of high-frequency electromagnetic wavescalled millimeter waves is currently under development. The wavelengthof millimeter waves is 10 mm to 1 mm and the frequency of millimeterwaves is 30 GHz to 300 GHz, and assignment of a channel in units of G′Hzis feasible in a 60-GHz band or the like, for example.

Generally, millimeter waves have characteristics that they propagatemore straightly and are attenuated by reflection more significantlycompared to microwaves. Therefore, a radio communication path inmillimeter-wave communication are mainly formed with direct waves orreflected waves reflected once or so. Millimeter waves also havecharacteristics that a free space propagation loss is large (anelectric, wave attainment distance is short). Therefore, while radiocommunication using millimeter waves has an advantage that spacedivision can be performed easier than the case of using microwaves,there is an aspect that a communication distance is short.

In order to compensate for such a weakness of millimeter waves and makeuse of high-speed radio communication using millimeter waves in a largervariety of scenes, one approach is to add a directionality to antennasof transmitting and receiving devices and aim a transmitting beam and areceiving beam in the direction where a device at the other end ofcommunication is located to thereby lengthen a communication distance.The directionality of a beam can be controlled by mounting a pluralityof antennas on transmitting and receiving devices and assigningdifferent weights to the respective antennas, for example. JapaneseUnexamined Patent Application Publication No. 2000-307494, for example,discloses a technique of performing radio communication with millimeterwaves after exchanging a control signal through a communication mediumsuch as sound waves, infrared rays, light or the like and learning anoptimum antenna directionality.

SUMMARY OF THE INVENTION

However, the technique of learning an optimum antenna directionalityfirstly changes an antenna directionality at the transmitting end eachtime transmitting and receiving one packet and secondary determines anoptimum directionality at the receiving end according to a result of thereceived packet. In this case, it is necessary to transmit and receivethe same number of packets as the number of beam patterns, whichincreases the time for learning and may cause degradation of thethroughput.

In light of the foregoing, it is desirable to provide a novel andimproved communication device, communication control method andcommunication system that enable high-speed learning of an antennadirectionality to be used for millimeter-wave communication.

According to an embodiment of the present invention, there is provided acommunication device including: a first radio communication unit capableof radio communication in accordance with a first communication method;and a second radio communication unit capable of radio communication inaccordance with a second communication method using a higher frequencyband than the first communication method, wherein the first radiocommunication unit transmits an instruction signal instructing to learna beam directionality to another communication device, and the secondradio communication unit transmits a beam reference signal used forlearning a beam directionality to said another communication deviceafter completion of transmission of the instruction signal by the firstradio communication unit and before reception of a response signal tothe instruction signal.

The second radio communication unit may transmit the beam referencesignal after a prescribed time period has elapsed from completion oftransmission of the instruction signal by the first radio communicationunit.

The instruction signal may contain only a header portion of a signalformat conforming to the first communication method.

The beam reference signal may be a signal containing plural signalsequences respectively associated with different directionalitypatterns.

The beam reference signal may be a signal containing plural time slotsrespectively corresponding to the plural signal sequences.

The beam reference signal may be a signal combining the plural signalsequences in orthogonal or pseudo orthogonal relation with one another.

At least part of transmission processing of a radio signal in accordancewith the first communication method and at least part of transmissionprocessing of a radio signal in accordance with the second communicationmethod may be executed using a common circuit.

According to another embodiment of the present invention, there isprovided a communication device including: a first radio communicationunit capable of radio communication in accordance with a firstcommunication method; and a second radio communication unit capable ofradio communication in accordance with a second communication methodusing a higher frequency band than the first communication method,wherein after the first radio communication unit transmits aninstruction signal instructing to learn a beam directionality to anothercommunication device, the first radio communication unit transmits abeam reference signal used for learning a transmitting beamdirectionality of the second radio communication unit to said anothercommunication device before receiving a response signal to theinstruction signal.

The first radio communication unit may further receive a notificationsignal containing a parameter value for specifying an optimum beampattern determined based on the beam reference signal from said anothercommunication device, and the second radio communication unit mayperform radio communication with said another communication device byusing a beam pattern specified by the parameter value contained in thenotification signal.

According to another embodiment of the present invention, there isprovided a communication device including: a first radio communicationunit capable of radio communication in accordance with a firstcommunication method; and a second radio communication unit capable ofradio communication in accordance with a second communication methodusing a higher frequency band than the first communication method,wherein upon receiving an instruction signal instructing to learn a beamdirectionality, the first radio communication unit determines a certaintime point after completion of reception of the instruction signal andbefore transmission of a response signal to the instruction signal as areception start time point of a beam reference signal, and the secondradio communication unit starts reception of the beam reference signalfrom the reception start time point determined by the first radiocommunication unit and determines a parameter value for specifying anoptimum beam pattern based on the received beam reference signal.

The reception start time point may be a time point after a prescribedtime period has elapsed from completion of reception of the instructionsignal by the first radio communication unit.

At least part of reception processing of a radio signal in accordancewith the first communication method and at least part of receptionprocessing of a radio signal in accordance with the second communicationmethod may be executed using a common circuit.

According to another embodiment of the present invention, there isprovided a communication device including: a first radio communicationunit capable of radio communication in accordance with a firstcommunication method; and a second radio communication unit capable ofradio communication in accordance with a second communication methodusing a higher frequency band than the first communication method,wherein upon receiving an instruction signal instructing to learn a beamdirectionality, the first radio communication unit further receives abeam reference signal transmitted subsequent to the instruction signaland used for learning a transmitting beam directionality to be used forradio communication by the second radio communication unit, anddetermines a parameter value for specifying an optimum beam patternbased on the received beam reference signal.

The first radio communication unit may determine the parameter value forspecifying an optimum beam pattern in accordance with eigenvalueanalysis based on the beam reference signal.

According to another embodiment of the present invention, there isprovided a communication control method between a transmitting deviceand a receiving device capable of radio communication in accordance witha first communication method and a second communication method using ahigher frequency band than the first communication method, including thesteps of: transmitting an instruction signal instructing to learn a beamdirectionality from the transmitting device to the receiving device inaccordance with the first communication method; transmitting a beamreference signal used for learning a beam directionality from thetransmitting device to the receiving device in accordance with thesecond communication method after completing transmission of theinstruction signal and before receiving a response signal to theinstruction signal; starting reception of the beam reference signal froma prescribed reception start time point determined based on the receivedinstruction signal in the receiving device; and determining a parameterfor specifying a beam having an optimum directionality based on thereceived beam reference signal.

According to another embodiment of the present invention, there isprovided a communication system including a transmitting device and areceiving device respectively including: a first radio communicationunit capable of radio communication in accordance with a firstcommunication method; and a second radio communication unit capable ofradio communication in accordance with a second communication methodusing a higher frequency band than the first communication method,wherein the first radio communication unit of the transmitting devicetransmits an instruction signal instructing to learn a beamdirectionality to the receiving device, the second radio communicationunit of the transmitting device transmits a beam reference signal usedfor learning a beam directionality to the receiving device aftercompletion of transmission of the instruction signal by the first radiocommunication unit and before reception of a response signal to theinstruction signal, upon receiving the instruction signal, the firstradio communication unit of the receiving device determines a receptionstart time point of the beam reference signal based on the instructionsignal, and the second radio communication unit of the receiving devicestarts reception of the beam reference signal from the determinedreception start time point and determines a parameter value forspecifying an optimum beam pattern based on the received beam referencesignal.

According to the embodiments of the present invention described above,it is possible to provide a communication device, a communicationcontrol method and a communication system that enable high-speedlearning of an antenna directionality to be used for millimeter-wavecommunication.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view showing an overview of a communication systemaccording to an embodiment.

FIG. 2 is a block diagram showing an example of a configuration of atransmitting device according to a first embodiment.

FIG. 3 is a block diagram showing an example of a specific configurationof a second digital unit in the transmitting device according to thefirst embodiment.

FIG. 4 is an explanatory view showing an example of beam patterns.

FIG. 5 is an explanatory view showing an example of formats of aninstruction signal and a beam reference signal.

FIG. 6 is a block diagram showing an example of a configuration of areceiving device according to the first embodiment.

FIG. 7 is a block diagram showing an example of a specific configurationof a second digital unit in the receiving device according to the firstembodiment.

FIG. 8 is an explanatory view to describe directionality controlprocessing.

FIG. 9 is an explanatory view showing an example of a signaltransmitting and receiving sequence according to the first embodiment.

FIG. 10 is an explanatory view showing another example of a format of abeam reference signal according to the first embodiment.

FIG. 11 is a block diagram showing an example of a configuration of atransmitting device according to a second embodiment.

FIG. 12 is a block diagram showing an example of a specificconfiguration of a second digital unit in the transmitting deviceaccording to the second embodiment.

FIG. 13 is an explanatory view to describe the timing of transmitting abeam reference signal according to the second embodiment.

FIG. 14 is a block diagram showing an example of a configuration of areceiving device according to the second embodiment.

FIG. 15 is a block diagram showing an example of a specificconfiguration of a second digital unit in the receiving device accordingto the second embodiment.

FIG. 16 is a block diagram showing an example of a configuration of atransmitting device according to a third embodiment.

FIG. 17 is an explanatory view showing an example of formats of aninstruction signal and a beam reference signal according to the thirdembodiment.

FIG. 18 is a block diagram showing an example of a configuration of areceiving device according to the third embodiment.

FIG. 19 is a block diagram showing an example of a specificconfiguration of a first digital unit in the receiving device accordingto the third embodiment.

FIG. 20 is a block diagram showing an example of a specificconfiguration of a second digital unit in the receiving device accordingto the third embodiment.

FIG. 21 is an explanatory view showing an example of a signaltransmitting and receiving sequence according to the third embodiment.

DETAILED DESCRIPTION OF THE EMBODIMENT(S)

Hereinafter, preferred embodiments of the present invention will bedescribed in detail with reference to the appended drawings. Note that,in this specification and the appended drawings, structural elementsthat have substantially the same function and structure are denoted withthe same reference numerals, and repeated explanation of thesestructural elements is omitted.

Preferred embodiments of the present invention will be describedhereinafter in the following order.

1. Overview of Communication System

2. Explanation of First Embodiment

-   -   2-1. Configuration of Transmitting Device    -   2-2. Configuration of Receiving Device    -   2-3. Example of Signal Transmitting and Receiving Sequence    -   2-4. Alternative Example

3. Explanation of Second Embodiment

-   -   3-1. Configuration of Transmitting Device    -   3-2. Configuration of Receiving Device

4. Explanation of Third Embodiment

-   -   4-1. Configuration of Transmitting Device    -   4-2. Configuration of Receiving Device    -   4-3. Example of Signal Transmitting and Receiving Sequence    -   4-4. Alternative Example

5. Summary

1. Overview of Communication System

FIG. 1 is a schematic view showing an overview of a communication system1 according to an embodiment of the present invention. Referring to FIG.1, the communication system 1 includes a communication device 100 and acommunication device 200. In this embodiment, the communication device100 transmits a given signal, which is described later, to thecommunication device 200 and starts communication with the communicationdevice 200. The communication device 200 receives a signal transmittedfrom the communication device 100 and starts communication with thecommunication device 100. Therefore, in this specification, thecommunication device 100 is referred to as a device at the transmittingend or a transmitting device, and the communication device 200 isreferred to as a device at the receiving end or a receiving device, insome cases.

The communication devices 100 and 200 can perform radio communicationwith each other in accordance with first and second communicationmethods. The first communication method is a communication method usingelectromagnetic waves such as microwaves, for example, that propagateless straightly and are attenuated by reflection less significantlycompared to the above-described millimeter waves. The firstcommunication method may be a communication method based on wireless LAN(Local Area Network) standards such as IEEE802.11a/b/g, for example.Thus, when performing radio communication in accordance with the firstcommunication method, the communication devices 100 and 200 cancommunicate with each other without considering the directionality of atransmitting beam and a receiving beam. On the other hand, the secondcommunication method is a communication method using electromagneticwaves that propagate straightly and are attenuated by reflectionsignificantly, which are typified by the above-described millimeterwaves. The second communication method may be a communication methodbased on VHT (Very High Throughput) standards using a 60-GHz band, forexample. Thus, when performing radio communication in accordance withthe second communication method, it is preferred that the communicationdevices 100 and 200 transmit and receive radio signals by pointing atransmitting beam and a receiving beam at the device at the other end ofcommunication.

In the example of FIG. 1, the communication device 100 includes anantenna 110 for transmitting and receiving radio signals in accordancewith the first communication method and a plurality of antennas 160 a to160 n for transmitting and receiving radio signals in accordance withthe second communication method. The communication device 200 includesan antenna 210 for transmitting and receiving radio signals inaccordance with the first communication method and a plurality ofantennas 260 a to 260 n for transmitting and receiving radio signals inaccordance with the second communication method. The communicationdevices 100 and 200 can perform so-called MIMO (Multi-InputMulti-Output) communication in accordance with the second communicationmethod by using the plurality of antennas 160 a to 160 n and theplurality of antennas 260 a to 260 n. By adjusting weights assigned tosignals transmitted and received through the respective antennas, thedirectionality of transmitting and receiving beams at the time of radiocommunication in accordance with the second communication method iscontrolled. Referring to FIG. 1, a transmitting beam Bt is directed fromthe communication device 100 toward the communication device 200, forexample. Further, a receiving beam Br is directed from the communicationdevice 200 toward the communication device 100, for example.

The communication devices 100 and 200 may be a PC (Personal Computer), aterminal device such as a cellular phone terminal, a portableinformation terminal, a music player or a game terminal or a householdelectrical appliance such as a television set, for example. Further, thecommunication devices 100 and 200 may be network equipment such as abroadband router or a wireless access point. Furthermore, thecommunication devices 100 and 200 may be a radio communication moduleincorporated into such equipment, for example.

2. Explanation of First Embodiment

Configurations of the communication devices according to a firstembodiment of the present invention are described hereinafter withreference to FIGS. 2 to 8.

2-1. Configuration of Transmitting Device

FIG. 2 is a block diagram showing an example of a configuration of thecommunication device 100 according to the embodiment. Referring to FIG.2, the communication device 100 includes an antenna 110, a first radiocommunication unit 120, a storage unit 150, a plurality of antennas 160a to 160 n and a second radio communication unit 170. The first radiocommunication unit 120 includes a first analog unit 122, an AD(Analog-to-Digital) conversion unit 124, a DA (Digital-to-Analog)conversion unit 126, a first digital unit 130 and a control unit 140.The second radio communication unit 170 includes a second analog unit172, an AD conversion unit 174, a DA conversion unit 176, a seconddigital unit 180 and a control unit 190.

The antenna 110 is an antenna that is used for radio communication inaccordance with the first communication method. The antenna 110transmits an instruction signal which instructs to learn a beamdirectionality by using microwaves, for example. Further, the antenna110 receives a notification signal to obtain notification of an optimumbeam pattern and outputs it to the first analog unit 122, for example.

The first analog unit 122 typically corresponds to an RF (RadioFrequency) circuit for transmitting and receiving a radio signal inaccordance with the first communication method. Specifically, the firstanalog unit 122 performs amplification and frequency conversion of areceived signal received by the antenna 110 and outputs the signal tothe AD conversion unit 124, for example. Further, the first analog unit122 performs frequency conversion of a transmission signal convertedinto an analog signal by the DA conversion unit 126 and outputs thesignal to the antenna 110.

The AD conversion unit 124 converts an analog received signal input fromthe first analog unit 122 into a digital signal and outputs it to thefirst digital unit 130. The DA conversion unit 126 converts a digitaltransmission signal input from the first digital unit 130 into an analogsignal and outputs it to the first analog unit 122.

The first digital unit 130 typically includes a circuit for demodulatingand decoding a received signal in accordance with the firstcommunication method and a circuit for encoding and modulating atransmission signal in accordance with the first communication method.If the instruction signal which instructs to learn a beam directionalityis input from the control unit 140, the first digital unit 130 encodesand modulates the instruction signal and outputs it to the DA conversionunit 126, for example. Further, if the above-described notificationsignal is input from the AD conversion unit 124, the first digital unit130 demodulates and decodes the notification signal and outputs it tothe control unit 140, for example.

The control unit 140 controls the overall operation of the first radiocommunication unit 120 by using an arithmetic unit such as a CPU(Central Processing Unit), for example. The control unit 140 outputs theabove-described instruction signal to the first digital unit 130 inresponse to a request from a given application, for example. Further, ifa decoded notification signal is input from the first digital unit 130,the control unit 140 acquires a parameter value for specifying anoptimum beam pattern contained in the notification signal and stores itinto the storage unit 150.

The storage unit 150 stores a program and a parameter value to be usedfor communication processing by the communication device 100 by using arecording medium such as semiconductor memory, for example. In thisembodiment, the storage unit 150 may store a parameter value forspecifying an optimum beam pattern at the time of radio communication bythe second radio communication unit 170 in accordance with the secondcommunication method, for example.

The plurality of antennas 160 a to 160 n are antennas to be used forradio communication in accordance with the second communication method.The plurality of antennas 160 a to 160 n are typically configured asMIMO antennas. Specifically, the antennas 160 a to 160 n transmit radiosignals which are weighted with prescribed weighting factors by usingmillimeter waves, for example. Further, the antennas 160 a to 160 nreceive radio signals, which are millimeter waves, and output thesignals to the second analog unit 172, for example.

The second analog unit 172 typically corresponds to an RF circuit fortransmitting and receiving radio signals in accordance with the secondcommunication method. Specifically, the second analog unit 172 performsamplification and frequency conversion of a plurality of receivedsignals respectively received by the antennas 160 a to 160 n and outputsthe signals to the AD conversion unit 174, for example. Further, thesecond analog unit 172 performs frequency conversion of a plurality oftransmission signals respectively converted into analog signals by theDA conversion unit 176 and outputs the signals to the antennas 160 a to160 n.

The AD conversion unit 174 converts a plurality of analog receivedsignals input from the second analog unit 172 into digital signals andoutputs them to the second digital unit 180. The DA conversion unit 176converts a plurality of digital transmission signals input from thesecond digital unit 180 into analog signals and outputs them to thesecond analog unit 172.

The second digital unit 180 typically includes a circuit fordemodulating and decoding received signals in accordance with the secondcommunication method and a circuit for encoding and modulatingtransmission signals in accordance with the second communication method.

FIG. 3 is a block diagram showing an example of a specific configurationof the second digital unit 180. Referring to FIG. 3, the second digitalunit 180 includes a synchronization unit 181, a receiving beamprocessing unit 182, a demodulation and decoding unit 183, an encodingand modulation unit 184, and a transmitting beam processing unit 185.

The synchronization unit 181 synchronizes the start timing of receptionprocessing on as plurality of received signals received by the pluralityof antennas 160 a to 160 n according to a preamble at the head of apacket, for example, and outputs the signals to the receiving beamprocessing unit 182.

The receiving beam processing unit 182 performs weighting processing ofthe plurality of received signals input from the synchronization unit181 according to uniform distribution or Taylor distribution, forexample, and thereby controls the directionality of a receiving beam.The values of the weights used by the receiving beam processing unit 182are specified by a directionality control signal input from the controlunit 190, for example. Alternatively, the receiving beam processing unit182 may produce a receiving beam by treating the plurality of antennas160 a to 160 n as an array antenna.

The demodulation and decoding unit 183 demodulates and decodes thereceived signals weighted by the receiving beam processing unit 182according to arbitrary modulation method and encoding method used in thesecond communication method and acquires a data signal. The demodulationand decoding unit 183 then outputs the acquired data signal to thecontrol unit 190.

The encoding and modulation unit 184 encodes and modulates a data signalinput from the control unit 190 according to arbitrary encoding methodand modulation method used in the second communication method andgenerates a transmission signal. The encoding and modulation unit 184then outputs the generated transmission signal to the transmitting beamprocessing unit 185.

The transmitting beam processing unit 185 generates a plurality oftransmission signals weighted according to uniform distribution orTaylor distribution, for example, from a transmission signal input fromthe encoding and modulation unit 184 and thereby controls thedirectionality of a transmitting beam. The values of the weights used bythe transmitting beam processing unit 185 are specified by adirectionality control signal input from the control unit 190, forexample. Alternatively, the transmitting beam processing unit 185 mayproduce a transmitting beam by treating the plurality of antennas 160 ato 160 n as an array antenna. The plurality of transmission signalsweighted by the transmitting beam processing unit 185 is respectivelyoutput to the DA conversion unit 176.

Although not shown in FIG. 3, the second digital unit 180 may furtherestimate channel characteristics of MIMO channels from the receivedsignals received by the plurality of antennas 160 a to 160 n and performchannel equalization according to the estimation result.

Referring back to FIG. 2, an example of a configuration of thecommunication device 100 is further described.

The control unit 190 controls the overall operation of the second radiocommunication unit 170 by using an arithmetic unit such as a CPU, forexample. The control unit 190 makes control to transmit a beam referencesignal from the second radio communication unit 170 after completingtransmission of the above-described instruction signal from the firstradio communication unit 120 and before receiving a response signal tothe instruction signal in response to a request from a givenapplication, for example. Further, the control unit 190 acquires aparameter value for specifying an optimum beam pattern from the storageunit 150 and outputs a directionality control signal that contains theacquired parameter value to the receiving beam processing unit 182 orthe transmitting beam processing unit 185 of the second digital unit 180described above. A receiving beam or a transmitting beam at the time ofradio communication in accordance with the second communication methodby the communication device 100 is thereby directed in the directionwhere the device at the other end of communication is located.

FIG. 4 is an explanatory view showing an example of beam patterns whichcan be created in the communication device 100.

Referring to FIG. 4, ten transmitting beam patterns Bt0 to Bt9 are shownwhich can be created in the communication device 100 according to thepresent embodiment. The transmitting beam patterns Bt0 to Bt9respectively have directionalities in directions differing by 36 degreeseach on a plane where the communication device 100 is located. Thetransmitting beam processing unit 185 of the communication device 100can transmit radio signals from the antennas 160 a to 160 n by using atransmitting beam pattern selected from the ten transmitting beampatterns Bt0 to Bt9 according to the directionality control signal fromthe control unit 190. Further, receiving beam patterns which can becreated in the communication device 100 may be beam patterns similar tothe transmitting beam patterns Bt0 to Bt9 shown in FIG. 4. In thestorage unit 150 of the communication device 100, weighting factors forthe antennas 160 a to 160 n to create those beam patterns are prestored.It should be noted that the transmitting beam patterns and the receivingbeam patterns which can be created in the communication device 100 arenot limited such examples. For example, the transmitting beam patternsor the receiving beam patterns having directionalities in variousdirections on a three-dimensional space may be created.

FIG. 5 is an explanatory view showing an example of signal formats ofthe instruction signal and the beam reference signal transmitted fromthe communication device 100.

Referring to FIG. 5, the instruction signal transmitted from the antenna110 in accordance with the first communication method contains only aheader portion 112 of the signal format conforming to the firstcommunication method. A data portion 118 of the signal format conformingto the first communication method is omitted in the instruction signal.By omitting the data portion 118 in the instruction signal in thismanner, it is possible to promptly complete transmission of theinstruction signal and promptly start transmission of the beam referencesignal in accordance with the second communication method, for example.The header portion 112 has L-STF (Legacy-Short Training Field) 114 andL-LTF (Legacy-Long Training Field) 116, for example. The L-STF 114principally serves as a preamble and can be used for packet detection,automatic gain control and synchronization processing at the receivingend. The L-LTF 116 is principally used for channel estimation andfrequency offset correction.

On the other hand, the beam reference signal transmitted from theantennas 160 a to 160 n has BTF (Beam Training Field) 162. The BTF 162is transmitted from the antennas 160 a to 160 n under control by thecontrol unit 190 at the timing when the data portion 118 would betransmitted in the case where the data portion 118 of the instructionsignal described above is not omitted.

In this embodiment, the BTF 162 is composed of ten time slots T0 to T9respectively corresponding to the transmitting beam patterns Bt0 to Bt9shown in FIG. 4. In each time slots T0 to T9, a known signal sequenceused for learning of a beam at the receiving end is weighted withweighting factors for creating the corresponding transmitting beampatterns Bt0 to Bt9, respectively. Specifically, the directionality ofthe transmitting beam of the beam reference signal is sequentiallychanged in the respective time slots T0 to T9. Accordingly, in areceiving device located in the vicinity of the communication device100, a power level of a received signal has an outstanding value in anytime slot of the beam reference signal according to the location, sothat an optimum transmitting beam pattern can be determined. The knownsignal sequence may be a random pattern of BPSK (Binary Phase ShiftKeying), for example.

As the instruction signal shown in FIG. 5, a header portion of RTS(Request To Send) or CTS (Clear To Send) based on IEEE802.11a/b/gstandards or the like may be used, for example. As an example, atransmitting and receiving sequence of a signal in which the headerportion of RTS is the instruction signal is described in further detaillater.

A configuration of the communication device 200 that receives theinstruction signal and the beam reference signal transmitted in theabove manner is described hereinafter.

2-2. Configuration of Receiving Device

FIG. 6 is a block diagram showing an example of a configuration of thecommunication device 200 according to the first embodiment. Referring toFIG. 6, the communication device 200 includes the antenna 210, a firstradio communication unit 220, a storage unit 250, a plurality ofantennas 260 a to 260 n and a second radio communication unit 270. Thefirst radio communication unit 220 includes a first analog unit 222, anAD conversion unit 224, a DA conversion unit 226, a first digital unit230 and a control unit 240. The second radio communication unit 270includes a second analog unit 272, an AD conversion unit 274, a DAconversion unit 276, a second digital unit 280 and a control unit 290.

The antenna 210 is an antenna that is used for radio communication inaccordance with the first communication method. The antenna 210 receivesthe above-described instruction signal that is transmitted from thecommunication device 100, for example. Further, the antenna 210transmits a notification signal for giving notification of an optimumbeam pattern that is determined by processing which is described later,for example.

The first analog unit 222 typically corresponds to an RF circuit fortransmitting and receiving a radio signal in accordance with the firstcommunication method. Specifically, the first analog unit 222 performsamplification and frequency conversion of a received signal received bythe antenna 210 and outputs the signal to the AD conversion unit 224,for example. Further, the first analog unit 222 performs frequencyconversion of a transmission signal converted into an analog signal bythe DA conversion unit 226 and outputs the signal to the antenna 210.

The AD conversion unit 224 converts an analog received signal input fromthe first analog unit 222 into a digital signal and outputs it to thefirst digital unit 230. The DA conversion unit 226 converts a digitaltransmission signal input from the first digital unit 230 into an analogsignal and outputs it to the first analog unit 222.

The first digital unit 230 typically includes a circuit for demodulatingand decoding a received signal in accordance with the firstcommunication method and a circuit for encoding and modulating atransmission signal in accordance with the first communication method.Further, in this embodiment, if the above-described instruction signalis input, the first digital unit 230 acquires synchronization by usingthe header portion 112 of the instruction signal shown in FIG. 5 andnotifies a reception start time point at which reception of the beamreference signal is to be started to the second digital unit 280 of thesecond radio communication unit 270. For example, it is assumed that atime interval from a given position (e.g. at the head of the L-STF 114,at the head of the L-LTF 116 or at the end of the L-LTF 116 etc.) of theheader portion 112 of the instruction signal to the head of the beamreference signal is prescribed in advance between a transmitting deviceand a receiving device. In such a case, the first digital unit 230 candetermine a time point at which the prescribed time interval has elapsedfrom the time point at which the given position of the header portion112 of the instruction signal is detected as the reception start timepoint. Alternatively, for example, data that designates a specificreception start time point may be contained in the header portion 112 ofthe instruction signal in a transmitting device. In such a case, thefirst digital unit 230 can acquire the data that designates thereception start time point from the header portion 112 of theinstruction signal and determine the reception start time point based onthe data. Reception processing of the beam reference signal in thesecond digital unit 280 is described in further detail later. Then, if anotification signal for notifying the optimum beam pattern determinedusing the beam reference signal is input from the control unit 240, thefirst digital unit 230 encodes and modulates the notification signal andoutputs it to the DA conversion unit 226, for example.

The control unit 240 controls the overall operation of the first radiocommunication unit 220 by using an arithmetic unit such as a CPU, forexample. Further, if the optimum beam pattern is determined by thesecond radio communication unit 270, which is described later, thecontrol unit 240 acquires a parameter value that specifies thedetermined optimum beam pattern from the storage unit 250, adds theparameter value to the above-described notification signal and outputsthe signal to the first digital unit 230.

The storage unit 250 stores a program and a parameter value to be usedfor communication processing by the communication device 200 by using arecording medium such as semiconductor memory, for example. In thisembodiment, the storage unit 250 may store a parameter value forspecifying an optimum beam pattern at the time of radio communication bythe second radio communication unit 270 in accordance with the secondcommunication method, for example. Further, the storage unit 250 storesa parameter value for specifying an optimum beam pattern at thetransmitting end that is determined by the second radio communicationunit 270, which is described later, for example.

The plurality of antennas 260 a to 260 n are antennas to be used forradio communication in accordance with the second communication method.The plurality of antennas 260 a to 260 n are typically configured asMIMO antennas. Specifically, the antennas 260 a to 260 n transmit radiosignals which are weighted with prescribed weighting factors by usingmillimeter waves, for example. Further, the antennas 260 a to 260 nreceive radio signals, which are millimeter waves, and output thesignals to the second analog unit 272, for example.

The second analog unit 272 typically corresponds to an RF circuit fortransmitting and receiving radio signals in accordance with the secondcommunication method. Specifically, the second analog unit 272 performsamplification and frequency conversion of a plurality of receivedsignals respectively received by the antennas 260 a to 260 n and outputsthe signals to the AD conversion unit 274, for example. Further, thesecond analog unit 272 performs frequency conversion of a plurality oftransmission signals respectively converted into analog signals by theDA conversion unit 276 and outputs the signals to the antennas 260 a to260 n.

The AD conversion unit 274 converts a plurality of analog receivedsignals input from the second analog unit 272 into digital signals andoutputs them to the second digital unit 280. The DA conversion unit 276converts a plurality of digital transmission signals input, from thesecond digital unit 280 into analog signals and outputs them to thesecond analog unit 272.

The second digital unit 280 typically includes a circuit fordemodulating and decoding received signals in accordance with the secondcommunication method and a circuit for encoding and modulatingtransmission signals in accordance with the second communication method.

FIG. 7 is a block diagram showing an example of a specific configurationof the second digital unit 280. Referring to FIG. 7, the second digitalunit 280 includes a synchronization unit 281, a receiving beamprocessing unit 282, a power calculation unit 283, a determination unit284, a demodulation and decoding unit 285, an encoding and modulationunit 286 and a transmitting beam processing unit 287.

The synchronization unit 281 synchronizes the start timing of receptionprocessing on a plurality of received signals received by the pluralityof antennas 260 a to 260 n according to a preamble at the head of apacket, for example, and outputs the signals to the receiving beamprocessing unit 282. Further, if the reception start time point of thebeam reference signal is notified from the first digital unit 230 of thefirst radio communication unit 220 described above, the synchronizationunit 281 starts reception of the beam reference signal illustrated inFIG. 5 from the notified reception start time point. Then, thesynchronization unit 281 outputs the received beam reference signal tothe receiving beam processing unit 282 and instructs calculation of areceived power to the power calculation unit 283.

The receiving beam processing unit 282, like the receiving beamprocessing unit 182 described above, performs weighting processing ofthe plurality of received signals input from the synchronization unit281 according to uniform distribution or Taylor distribution, forexample, and thereby controls the directionality of a receiving beam.The receiving beam processing unit 282 then outputs the weightedreceived signal to the power calculation unit 283 and the demodulationand decoding unit 285.

FIG. 8 is an explanatory view to describe directionality controlprocessing of q receiving beam by the receiving beam processing unit282.

Referring to FIG. 8, an example of the signal format of the beamreference signal is shown which is transmitted from the communicationdevice 100 in accordance with the second communication method. The beamreference signal contains the BTF 162 composed of ten time slots T0 toT9 respectively corresponding to the transmitting beam patterns Bt0 toBt9. The receiving beam processing unit 282 further divides each of thetime slots T0 to T9 of the beam reference signal into ten sections ST0to ST9 and performs weighting processing of the received signals withten receiving beam patterns which are different from one another in therespective sections ST0 to ST9. For example, the first section ST0 ofthe time slot TO is associated with the receiving beam pattern Br0, andthe second section ST1 of the time slot TO is associated with thereceiving beam pattern Br1 or the like. As a result of suchdirectionality control processing, received signals transmitted andreceived with total 100 transmitting and receiving beam patterns (10transmitting beam patterns×10 receiving beam patterns) can be obtainedin one beam reference signal.

The power calculation unit 283 shown in FIG. 7 calculates receivedpowers of the respective received signals transmitted and received withthe above-described total 100 transmitting and receiving beam patternsin response to an instruction from the synchronization unit 281. Then,the power calculation unit 283 sequentially outputs the calculatedreceived power values to the determination unit 284.

The determination unit 284 determines a parameter value for specifyingthe optimum transmitting beam pattern and receiving beam pattern basedon the received power values input from the power calculation unit 283.The optimum beam pattern is a beam pattern with which a series ofreceived power values input from the power calculation unit 283 for onebeam reference signal has a maximum value. The parameter value forspecifying the optimum transmitting beam pattern may be any time slotnumber (T0 to T9) of the BTF 162 shown in FIG. 5 and FIG. 8, forexample. Alternatively, the parameter value for specifying the optimumtransmitting beam pattern may be a weighting factor to be multipliedwith a transmission signal by the transmitting beam processing unit 287,for example. Further, the parameter value for specifying the optimumtransmitting beam pattern may be a section number (ST0 to ST9) shown inFIG. 8, for example. Alternatively, the parameter value for specifyingthe optimum transmitting beam pattern may be weighting factors to berespectively multiplied with a plurality of received signals by thereceiving beam processing unit 282, for example. The determination unit284 outputs the determined parameter value to the control unit 290.

The demodulation and decoding unit 285 demodulates and decodes thereceived al weighted by the receiving beam processing unit 282 accordingto arbitrary modulation method and encoding method used in the secondcommunication method and acquires a data signal. The demodulation anddecoding unit 285 then outputs the acquired data signal to the controlunit 290.

The encoding and modulation unit 286 encodes and modulates the datasignal input from the control unit 290 according to arbitrary encodingmethod and modulation method used in the second communication method andgenerates a transmission signal. The encoding and modulation unit 286then outputs the generated transmission signal to the transmitting beamprocessing unit 287.

The transmitting beam processing unit 287, like the transmitting beamprocessing unit 185 described above, generates a plurality oftransmission signals weighted according to uniform distribution orTaylor distribution, for example, from the transmission signal inputfrom the encoding and modulation unit 286 and thereby controls thedirectionality of a transmitting beam. The values of the weights used bythe transmitting beam processing unit 287 are specified by adirectionality control signal input from the control unit 290, forexample. The plurality of transmission signals weighted by thetransmitting beam processing unit 287 is respectively output to the DAconversion unit 276.

Although not shown in FIG. 7, the second digital unit 280 may furtherestimate channel characteristics of MIMO channels from the receivedsignals received by the plurality of antennas 260 a to 260 n and performchannel equalization according to the estimation result.

Referring back to FIG. 6, an example of a configuration of thecommunication device 200 is further described.

The control unit 290 controls the overall operation of the second radiocommunication unit 270 by using an arithmetic unit such as a CPU, forexample. Further, if the beam reference signal is received by the secondradio communication unit 270, the control unit 290 stores a parametervalue for specifying an optimum transmitting beam pattern output fromthe second digital unit 280 into the storage unit 250. The storedparameter value is notified using a notification signal to a device fromwhich the beam reference signal has been transmitted (e.g. thecommunication device 100) by the first radio communication unit 220.Further, if a parameter value for specifying an optimum transmittingbeam pattern is output from the second digital unit 280, the controlunit 290 outputs a directionality control signal that contains theparameter value to the receiving beam processing unit 282 so as toproduce a receiving beam having a directionality in the direction of thedevice at the other end of communication. Further, the control unit 290may output a directionality control signal that contains the sameparameter value as the value used for producing the receiving beam tothe transmitting beam processing unit 287 so as to produce atransmitting beam having a directionality in the same direction. It isthereby possible to perform radio communication between thecommunication device 100 and the communication device 200 in accordancewith the second communication method with their directionalitiesoriented toward the other device, for example.

Instead of notifying the above-described parameter value from the secondradio communication unit 270 to the first radio communication unit 220through the storage unit 250, the parameter value may be notified fromthe second radio communication unit 270 to the first radio communicationunit 220 by using a dedicated signal line, for example.

2-3. Example of Signal Transmitting and Receiving Sequence

FIG. 9 is an explanatory view showing an example of a sequence ofsignals transmitted and received between the communication device 100and the communication device 200 described above. Referring to FIG. 9,signals transmitted from the communication device 100 (Tx) and thecommunication device 200 (Rx) are sequentially shown along the timeaxis.

First, the header portion of RTS in accordance with the firstcommunication method is transmitted from the first radio communicationunit 120 of the communication device 100. The header portion of RTScorresponds to the above-described instruction signal. Aftertransmission of the instruction signal is completed, BTF in accordancewith the second communication method is transmitted from the secondradio communication unit 170 of the communication device 100. The BTFcorresponds to the above-described beam reference signal. An optimumtransmitting beam pattern and an optimum receiving beam pattern fortransmitting a signal from the communication device 100 to thecommunication device 200 is thereby determined in the communicationdevice 200.

Next, CTS in accordance with the first communication method istransmitted from the first radio communication unit 220 of thecommunication device 200. The data portion of the CTS contains aparameter value that specifies an optimum transmitting beam pattern, forexample. In this case, the CTS corresponds to the above-describednotification signal. The communication device 100 can be therebynotified about the optimum transmitting beam pattern when transmitting asignal to the communication device 200. Note that the CTS transmittedfrom the communication device 200 to the communication device 100 mayalso serve as the above-described instruction signal. In this case, onlythe header portion of CTS (i.e. the instruction signal) is transmittedfrom the first radio communication unit 220 of the communication device200, and BTF in accordance with the second communication method istransmitted after completing transmission of the instruction signal. Anoptimum receiving beam pattern can be thereby determined in thecommunication device 100 as well.

After that, data is transmitted from the communication device 100 to thecommunication device 200, and ACK (acknowledgement) is transmitted backfrom the communication device 200 to the communication device 100. Atthis time, because the optimum transmitting and receiving beam patternsdetermined by learning are used between the communication device 100 andthe communication device 200, it is possible to transmit and receivedata more reliably in accordance with the second communication methodeven with use of millimeter waves with high straightness and shortelectric wave attainment distance.

2-4. Alternative Example

FIG. 10 is an explanatory view showing another example of the signalformat of the beam reference signal.

Referring to FIG. 10, the beam reference signal contains BTF 164. TheBTF 164 is a signal that combines a plurality of signal sequences inorthogonal or pseudo orthogonal relation with one another, which havedifferent directionality patterns. For instance, in the example of FIG.10, the BTF 164 is a signal that combines ten signal sequences which arerespectively spread by using spread codes C0 to C9 and respectivelycorrespond to the transmitting beam patterns Bt0 to Bt9. With use of thespread codes C0 to C9 that establish the orthogonal or pseudo orthogonalrelation, even if signal sequences associated with the transmitting beampatterns Bt0 to Bt9 are combined at the transmitting end, each signalsequence can be extracted from a composite signal at the receiving end.It is thereby possible to calculate a received power for each extractedsignal sequence and determine an optimum transmitting beam pattern withwhich the received power is maximum. In this case, a parameter forspecifying a transmitting beam pattern may be a spread code thatspecifies at least one signal sequence of the above-described signalsequences, an identifier of a signal sequence or the like, for example.The BTF 164, like the BTF 162 shown in FIG. 5, is transmitted inaccordance with the second communication method at the timing when thedata portion 118 would be transmitted in the case where the data portion118 of the instruction signal is not omitted. By using such analternative example, it is possible to shorten the data length of thebeam reference signal compared to the case of using the same number oftime slots as the number of beam patterns.

The first embodiment of the present invention is described above withreference to FIGS. 2 to 10. According to the present embodiment, thereception start time point of the beam reference signal that istransmitted in accordance with the second communication method (e.g.using millimeter waves etc.) is determined based on the instructionsignal transmitted in accordance with the first communication method(e.g. using microwaves or the like etc.). The beam reference signal istransmitted and received at the timing when the data portion omitted inthe instruction signal is originally supposed to be received. Then, aparameter value for specifying an optimum beam pattern is determinedbased on the beam reference signal. It is thereby possible to learnoptimum directionalities of transmitting and receiving beams used forradio communication in accordance with the second communication methodduring a time period in which one packet (e.g. RTS, CTS etc.) can betransmitted and received. Further, in this embodiment, a signal inaccordance with the first communication method and a signal inaccordance with the second communication method are not simultaneouslytransmitted, the possibility of an error caused by that signalprocessing in accordance with different communication methods isperformed at the same time is avoided.

3. Explanation of Second Embodiment

As described above, in the first embodiment, a signal in accordance withthe first communication method and a signal in accordance with thesecond communication method are not simultaneously transmitted.Therefore, a part of the circuit may be used in common by the firstradio communication unit and the second radio communication unit in eachcommunication device. As a second embodiment of the present invention, aconfiguration of a device in which a part of the circuit is used incommon by the first radio communication unit and the second radiocommunication unit is described hereinbelow. In this embodiment, adevice at the transmitting end (Tx), which is described in relation toFIG. 1, is a communication device 300, and a device at the receiving end(Rx) is a communication device 400.

3-1. Configuration of Transmitting Device

FIG. 11 is a block diagram showing an example of a configuration of thecommunication device 300 according to the second embodiment of thepresent invention. Referring to FIG. 11, the communication device 300includes an antenna 110, a first radio communication unit 320, a controlunit 340, a storage unit 150, a plurality of antennas 160 a to 160 n anda second radio communication unit 370. The first radio communicationunit 320 and the second radio communication unit 370 share the use of acommon analog unit 323, an AD/DA conversion unit 324, and a commondigital unit 331. Further, the first radio communication unit 320includes a first analog unit 322 and a first digital unit 330. Thesecond radio communication unit 370 includes a second analog unit 372and a second digital unit 380.

The first analog unit 322 receives a radio signal in a prescribedfrequency band that is used for the first communication method throughthe antenna 110, performs frequency conversion and outputs the signal tothe common analog unit 323, for example. Further, the first analog unit322 converts a transmission signal input from the common analog unit 323into a radio signal in a prescribed frequency band that is used for thefirst communication method and transmits the signal through the antenna110, for example.

If a received signal is input from the first analog unit 322, the commonanalog unit 323 amplifies the received signal, performs filtering andthen outputs the signal to the AD/DA conversion unit 324, for example.Further, if a transmission signal is input from the AD/DA conversionunit 324, the common analog unit 323 amplifies the transmission signaland outputs the signal to the first analog unit 322, for example.

If an analog received signal is input from the common analog unit 323,the AD/DA conversion unit 324 converts the received signal into adigital signal and outputs it to the first digital unit 330, forexample. Further, if a digital transmission signal is input from thefirst digital unit 330, the AD/DA conversion unit 324 converts thetransmission signal into an analog signal and outputs it to the commonanalog unit 323, for example.

If the digital received signal is input from the AD/DA conversion unit324, the first digital unit 330 performs reception processing specificto the first communication method, for example. The reception processingspecific to the first communication method may be arbitrary processingfor which commonality is not achievable between the first communicationmethod and the second communication method among reception processingsuch as packet synchronization, demodulation and decoding, for example.Next, if the received signal on which the reception processing specificto the first communication method has been performed is input from thefirst digital unit 330, the common digital unit 331 performs receptionprocessing for which commonality is achieved between the firstcommunication method and the second communication method. For example,if the same encoding method is used between the first communicationmethod and the second communication method, decoding processing amongthe reception processing can be performed in the common digital unit331. Then, the common digital unit 331 outputs a data signal acquired asa result of the reception processing to the control unit 340.

If a data signal for the first radio communication unit 320 is inputfrom the control unit 340, the common digital unit 331 performstransmission processing for which commonality is achieved between thefirst communication method and the second communication method. Forexample, if the same encoding method is used between the firstcommunication method and the second communication method, encodingprocessing among the transmission processing can be performed in thecommon digital unit 331. Next, the first digital unit 330 performstransmission processing specific to the first communication method, forexample. The transmission processing specific to the first communicationmethod may be arbitrary processing for which commonality is notachievable between the first communication method and the secondcommunication method among transmission processing such as encoding andmodulation, for example. Then, the first digital unit 330 outputs atransmission signal generated as a result of the transmission processingto the AD/DA conversion unit 324. Note that the order of processing inthe first digital unit 330 and the common digital unit 331 is notlimited to such an example.

The control unit 340 controls the overall operation of the first radiocommunication unit 320 and the second radio communication unit 370 byusing an arithmetic unit such as a CPU, for example. The control unit340 makes control to transmit the above-described instruction signalfrom the first radio communication unit 320 in response to a requestfrom a given application, for example. Then, the control unit 340 makescontrol to transmit the beam reference signal from the second radiocommunication unit 370 after completing transmission of the instructionsignal and before receiving a response signal to the instruction signal,for example. Further, if a decoded notification signal is input from thefirst digital unit 330, the control unit 340 acquires a parameter valuefor specifying an optimum beam pattern contained in the notificationsignal. Then, the control unit 340 outputs a directionality controlsignal that contains the acquired parameter value to a receiving beamprocessing unit 382 or a transmitting beam processing unit 385 of thesecond digital unit 380, which is described later.

The second analog unit 372 receives radio signals in a prescribedfrequency band that are used for the second communication method throughthe antennas 160 a to 160 n, performs frequency conversion and outputsthe signals to the common analog unit 323, for example. Further, thesecond analog unit 372 converts a plurality of transmission signalsinput from the common analog unit 323 into radio signals in a prescribedfrequency band that are used for the second communication method andtransmits the signals through the antennas 160 a to 160 n, for example.

If a plurality of received signals are input from the second analog unit372, the common analog unit 323 amplifies the plurality of receivedsignals, performs filtering and then outputs the signals to the AD/DAconversion unit 324, for example. Further, if a plurality oftransmission signals are input from the AD/DA conversion unit 324, thecommon analog unit 323 amplifies the plurality of transmission signalsand outputs the signals to the second analog unit 372, for example.

If a plurality of analog received signals are input from the commonanalog unit 323, the AD/DA conversion unit 324 converts the plurality ofreceived signals into digital signals and outputs them to the seconddigital unit 380, for example. Further, if a plurality of digitaltransmission signals are input from the second digital unit 380, theAD/DA conversion unit 324 converts the plurality of transmission signalsinto analog signals and outputs them to the common analog unit 323, forexample.

If a plurality of digital received signals are input from the AD/DAconversion unit 324, the second digital unit 380 performs receptionprocessing specific to the first communication method, for example.

FIG. 12 is a block diagram showing an example of a specificconfiguration of the second digital unit 380. Referring to FIG. 12, thesecond digital unit 380 includes a synchronization unit 181, a receivingbeam processing unit 382 and a transmitting beam processing unit 385.

The receiving beam processing unit 382 performs weighting processing ofthe plurality of received signals input from the synchronization unit181 according to uniform distribution or Taylor distribution, forexample, and thereby controls the directionality of a receiving beam.The values of the weights used by the receiving beam processing unit 382are specified by a directionality control signal input from the controlunit 340, for example. Alternatively, the receiving beam processing unit382 may produce a receiving beam by treating the plurality of antennas160 a to 160 n as an array antenna. The received signal weighted by thereceiving beam processing unit 382 is output to the common digital unit331.

The transmitting beam processing unit 385 generates a plurality oftransmission signals weighted according to uniform distribution orTaylor distribution, for example, from the transmission signal inputfrom the common digital unit 331 and thereby controls the directionalityof a transmitting beam. The values of the weights used by thetransmitting beam processing unit 385 are specified by a directionalitycontrol signal input from the control unit 340, for example.Alternatively, the transmitting beam processing unit 385 may produce atransmitting beam by treating the plurality of antennas 160 a to 160 nas an array antenna. The plurality of transmission signals weighted bythe transmitting beam processing unit 385 are respectively output to theAD/DA conversion unit 324. In this embodiment, beam patterns created inthe communication device 300 may be the beam patterns illustrated inFIG. 4 or other arbitrary beam patterns.

Referring back to FIG. 11, an example of a configuration of thecommunication device 300 according to the embodiment is furtherdescribed.

If the weighted received signal is input from the receiving beamprocessing unit 382 of the second digital unit 380, the common digitalunit 331 performs the reception processing for which commonality isachieved between the first communication method and the secondcommunication method, for example. For example, if the same modulationmethod and encoding method are used between the first communicationmethod and the second communication method, demodulation processing anddecoding processing among the reception processing can be performed inthe common digital unit 331. Then, the common digital unit 331 outputs adata signal acquired as a result of encoding processing to the controlunit 340.

If a data signal for the second radio communication unit 370 is inputfrom the control unit 340, the common digital unit 331 performstransmission processing for which commonality is achieved between thefirst communication method and the second communication method, forexample. If the same modulation method and encoding method are usedbetween the first communication method and the second communicationmethod, for example, encoding processing and modulation processing amongthe transmission processing can be performed in the common digital unit331. Then, the common digital unit 331 outputs a transmission signalgenerated as a result of encoding processing and modulation processingto the transmitting beam processing unit 385 of the second digital unit380. Note that the order of processing in the second digital unit 380and the common digital unit 331 is not limited to such an example.

FIG. 13 is an explanatory view to describe the timing of transmittingthe beam reference signal according to the embodiment.

Referring to FIG. 13, the instruction signal transmitted from theantenna 110 in accordance with the first communication method containsonly a header portion 112 of the signal format conforming to the firstcommunication method, as in the first embodiment. A data portion 118 ofthe signal format conforming to the first communication method isomitted in the instruction signal.

On the other hand, the beam reference signal transmitted from theantennas 160 a to 160 n has BTF 362. The BTF 362 is transmitted from theantennas 160 a to 160 n according to control by the control unit 340after predetermined time t has elapsed from completion of transmissionof the above-described instruction signal from the first radiocommunication unit 320. During the time t, the communication device 400that receives the instruction signal and the beam reference signal canswitch the operation of the common part of the circuit from an operationfor the first communication method to an operation for the secondcommunication method.

The BTF 362 is composed of ten time slots T0 to T9 respectivelycorresponding to the transmitting beam patterns Bt0 to Bt9 shown in FIG.4, for example, just like the BIT 162 according to the first embodiment.Accordingly, in the communication device 400, a power level of areceived signal has an outstanding value in any time slot of the beamreference signal according to the location, so that an optimumtransmitting beam pattern can be determined.

3-2. Configuration of Receiving Device

FIG. 14 is a block diagram showing an example of a configuration of thecommunication device 400 according to the second embodiment. Referringto FIG. 14, the communication device 400 includes an antenna 210, afirst radio communication unit 420, a control unit 440, a storage unit250, a plurality of antennas 260 a to 260 n and a second radiocommunication unit 470. The first radio communication unit 420 and thesecond radio communication unit 470 share the use of a common analogunit 423, an AD/DA conversion unit 424, and a common digital unit 431.Further, the first radio communication unit 420 includes a first analogunit 422 and a first digital unit 430. The second radio communicationunit 470 includes a second analog unit 472 and a second digital unit480.

The first analog unit 422 receives a radio signal in a prescribedfrequency band that is used for the first communication method throughthe antenna 210, performs frequency conversion and outputs the signal tothe common analog unit 423, for example. Further, the first analog unit422 converts a transmission signal input from the common analog unit 423into a radio signal in a prescribed frequency band that is used for thefirst communication method through the antenna 210, for example.

The common analog unit 423, like the common analog unit 323 of thecommunication device 300, performs amplification, filtering or the likeof a received signal and a transmission signal. Further, the AD/DAconversion unit 424, like the AD/DA conversion unit 324 of thecommunication device 300, performs conversion between an analog signaland a digital signal.

If a digital received signal is input from the AD/DA conversion unit424, the first digital unit 430 performs reception processing specificto the first communication method, for example. Next, if the receivedsignal on which the reception processing specific to the firstcommunication method has been performed is input from the first digitalunit 430, the common digital unit 431 performs the reception processingfor which commonality is achieved between the first communication methodand the second communication method, for example. Further, if theabove-described instruction signal is input, the first digital unit 430acquires synchronization by using the header portion 112 of theinstruction signal shown in FIG. 13 and notifies a reception start timepoint at which reception of the beam reference signal is to be startedto the second digital unit 480 of the second radio communication unit470. The reception start time point may be a time point at which thetime t shown in FIG. 13 has elapsed from completion of reception of theinstruction signal, for example.

If a data signal (e.g. the above-described notification signal etc.) forthe first radio communication unit 420 is input from the control unit440, the common digital unit 431 performs transmission processing forwhich commonality is achieved between the first communication method andthe second communication method, for example. Next, the first digitalunit 430 performs transmission processing specific to the firstcommunication method, for example. Note that the order of processing inthe first digital unit 430 and the common digital unit 431 is notlimited to such an example.

The control unit 440 controls the overall operation of the first radiocommunication unit 420 and the second radio communication unit 470 byusing an arithmetic unit such as a CPU, for example. If theabove-described instruction signal is received by the first radiocommunication unit 420, for example, the control unit 440 switches theoperation of the common analog unit 423, the AD/DA conversion unit 424and the common digital unit 431 to an operation in accordance with thesecond communication method. Such switch processing can be performedafter the instruction signal is received and until reception of the beamreference signal is started (i.e. during the time t shown in FIG. 13).Further, if an optimum beam pattern is determined by the second radiocommunication unit 470, which is described later, the control unit 440adds a parameter value that specifies the determined optimum beampattern to the notification signal and outputs the notification signalto the common digital unit 431 so as to transmit the notification signalfrom the first radio communication unit 420. Furthermore, the controlunit 440 outputs the above-described directionality control signal tothe second digital unit 480 and controls a transmitting beam and areceiving beam of the communication device 400.

The second analog unit 472 receives radio signals in a prescribedfrequency hand that are used for the second communication method throughthe antennas 260 a to 260 n, performs frequency conversion and outputsthe signals to the common analog unit 423, for example. Further, thesecond analog unit 472 converts a plurality of transmission signalsinput from the common analog unit 423 into radio signals in a prescribedfrequency band that are used for the second communication method andtransmits the signals through the antennas 260 a to 260 n, for example.

If a plurality of digital received signals are input from the AD/DAconversion unit 424, the second digital unit 480 performs receptionprocessing specific to the second communication method, for example.

FIG. 15 is a block diagram showing an example of a specificconfiguration of the second digital unit 480. Referring to FIG. 15, thesecond digital unit 480 includes a synchronization unit 281, a receivingbeam processing unit 482, a power calculation unit 283, a determinationunit 284 and a transmitting beam processing unit 487.

The receiving beam processing unit 482, like the receiving beamprocessing unit 382 described above, performs weighting processing ofthe plurality of received signals input from the synchronization unit281 according to uniform distribution or Taylor distribution, forexample, and thereby controls the directionality of a receiving beam.The receiving beam processing unit 482 then outputs the weightedreceived signal to the power calculation unit 283 and the common digitalunit 431. The directionality control processing of a receiving beam bythe receiving beam processing unit 482 may be similar to the processingaccording to the first embodiment described earlier with reference toFIG. 8.

The transmitting beam processing unit 487, like the above-describedtransmitting beam processing unit 385 described above, generates aplurality of transmission signals weighted according to uniformdistribution or Taylor distribution, for example, from the transmissionsignal input from the common digital unit 431 and output the signals tothe AD/DA conversion unit 424.

The configurations of the devices at the transmitting end and thereceiving end according to the second embodiment of the presentinvention are described above with reference to FIGS. 11 to 15.According to the embodiment, it is possible to learn thedirectionalities of transmitting and receiving beams used for radiocommunication in accordance with the second communication method at highspeed and further to suppress an increase in circuit scale by the shareduse of a part of the circuit used for transmission and receptionprocessing between the first and second communication methods. Further,because the beam reference signal used for learning of thedirectionality is received after a certain time interval from completionof reception of the instruction signal that instructs learning, it ispossible to switch the operation of the common part of the circuit fromthe first communication method to the second communication method duringthe time period.

4. Explanation of Third Embodiment

In the first and second embodiments described above, the optimumdirectionalities of transmitting and receiving beams when performingradio communication in accordance with the second communication methodare determined based on the beam reference signal conforming to thesecond communication method. If it is assumed that the arrival directionof direct waves or reflected waves with the highest received power doesnot vary regardless of whether a transmission medium is millimeter wavesor microwaves, the directionalities of transmitting and receiving beamsmay be learned by using microwaves (i.e. using the first communicationmethod). As a third embodiment of the present invention, a configurationof a device which transmits and receives the instruction signal and thebeam reference signal in accordance with the first communication methodand learns the directionalities of transmitting and receiving beams isdescribed hereinbelow. In this embodiment, a device at the transmittingend (Tx), which is described in relation to FIG. 1, is a communicationdevice 500, and a device at the receiving end (Rx) is a communicationdevice 600,

4-1. Configuration of Transmitting Device

FIG. 16 is a block diagram showing an example of a configuration of thecommunication device 500 according to the third embodiment of thepresent invention. Referring to FIG. 16, the communication device 500includes an antenna 110, a first radio communication unit 320, a controlunit 540, a storage unit 150, a plurality of antennas 160 a to 160 n anda second radio communication unit 370. The first radio communicationunit 320 and the second radio communication unit 370 share the use of acommon analog unit 323, an AD/DA conversion unit 324, and a commondigital unit 331. Further, the first radio communication unit 320includes a first analog unit 322 and a first digital unit 330. Thesecond radio communication unit 370 includes a second analog unit 372and a second digital unit 380.

The control unit 540 controls the overall operation of the first radiocommunication unit 320 and the second radio communication unit 370 byusing an arithmetic unit such as a CPU, for example. The control unit540 makes control to transmit an instruction signal which instructs tolearn a beam directionality from the first radio communication unit 320in response to a request from a given application, for example. Then,the control unit 540 makes control to transmit a beam reference signalused for learning of the directionality of a transmitting beam from thefirst radio communication unit 320 after completing transmission of theinstruction signal and before receiving a response signal to theinstruction signal, for example. Further, if a notification signal thatnotifies a learning result of the directionality is input from the firstradio communication unit 320, the control unit 540 acquires a parametervalue for specifying an optimum beam pattern contained in thenotification signal. Then, the control unit 540 outputs a directionalitycontrol signal that contains the acquired parameter value to a receivingbeam processing unit 382 or a transmitting beam processing unit 385 ofthe second digital unit 380.

FIG. 17 is an explanatory view to describe the timing of transmittingthe beam reference signal according to the embodiment.

Referring to FIG. 17, the instruction signal transmitted in accordancewith the first communication method by the first radio communicationunit 320 contains only a header portion 112 of the signal formatconforming to the first communication method, as in the first and secondembodiments.

On the other hand, the beam reference signal has BTF 562. In thisembodiment, the BTF 562 is transmitted subsequent to the above-describedinstruction signal by the first radio communication unit 320 inaccordance with the first communication method. The BTF 562 is composedof ten time slots T0 to T9 respectively corresponding to thetransmitting beam patterns Bt0 to Bt9 shown in FIG. 4, for example, justlike the BTF 162 according to the first embodiment and the BTF 362according to the second embodiment. Accordingly, in a receiving devicelocated in the vicinity of the communication device 500, a power levelof a received signal has an outstanding value in any time slot of thebeam reference signal according to the location, so that an optimumtransmitting beam pattern can be determined. In this manner, an optimumtransmitting beam pattern is determined based on the beam referencesignal transmitted in accordance with the first communication method.Then, the determined optimum transmitting beam pattern is applied to atransmitting beam pattern when performing radio communication inaccordance with the second communication method,

4-2. Configuration of Receiving Device

FIG. 18 is a block diagram showing an example of a configuration of thecommunication device 600 according to the third embodiment. Referring toFIG. 18, the communication device 600 includes an antenna 210, a firstradio communication unit 620, a control unit 640, a storage unit 250, aplurality of antennas 260 a to 260 n and a second radio communicationunit 670. The first radio communication unit 620 and the second radiocommunication unit 670 share the use of a common analog unit 423, anAD/DA conversion unit 424, and a common digital unit 431. Further, thefirst radio communication unit 620 includes a first analog unit 422 anda first digital unit 630. The second radio communication unit 670includes a second analog unit 472 and a second digital unit 680.

FIG. 19 is a block diagram showing an example of a specificconfiguration of the first digital unit 630. Referring to FIG. 19, thefirst digital unit 630 includes a synchronization unit 632, a powercalculation unit 634 and a determination unit 636.

The synchronization unit 632 detects a packet of a received signalreceived in accordance with the first communication method in accordancewith a preamble at the head of the packet, for example. Then, thesynchronization unit 632 outputs the received signal to the commondigital unit 431. Further, if the first digital unit 630 detects theabove-described instruction signal, it further detects the beamreference signal which is transmitted subsequent to the instructionsignal, outputs the detected beam reference signal to the powercalculation unit 634 and instructs calculation of a received power.

The power calculation unit 634 calculates received powers of theplurality of signal sequences contained the beam reference signal inresponse to an instruction from the synchronization unit 632. Theplurality of signal sequences may be signal sequences respectivelycontained in the time slots T0 to T9 described in relation to FIG. 17 orsignal sequences in orthogonal or pseudo orthogonal relation with oneanother described in relation to FIG. 10, for example. Then, the powercalculation unit 634 sequentially outputs the calculated received powersto the determination unit 636.

The determination unit 636 determines a parameter value for specifyingan optimum transmitting beam pattern based on the received power valuesinput from the power calculation unit 634. The optimum transmitting beampattern may be a transmitting beam pattern with which a series ofreceived power values are maximum values, for example. Then, thedetermination unit 636 outputs the parameter value determined based onthe received power values to the control unit 640.

The control unit 640 controls the overall operation of the first radiocommunication unit 620 and the second radio communication unit 670 byusing an arithmetic unit such as a CPU, for example. If the optimumtransmitting beam pattern is determined by the first radio communicationunit 620, for example, the control unit 640 adds a parameter value forspecifying the transmitting beam pattern to a notification signal andoutputs it to the common digital unit 431 so as to transmit thenotification signal from the first radio communication unit 620.Further, the control unit 640 may output a directionality control signalto the second digital unit 680 and controls a transmitting beam or areceiving beam of the communication device 600.

FIG. 20 is a block diagram showing an example of a specificconfiguration of the second digital unit 680. Referring to FIG. 20, thesecond digital unit 680 includes a synchronization unit 681, a receivingbeam processing unit 682 and a transmitting beam processing unit 487.

The synchronization unit 681 synchronizes the start timing of receptionprocessing on a plurality of received signals received in accordancewith the second communication method according to a preamble at the headof a packet, for example, and outputs the signals to the receiving beamprocessing unit 682.

The receiving beam processing unit 682 performs weighting processing ofthe plurality of received signals input from the synchronization unit681 according to uniform distribution or Taylor distribution, forexample, and thereby controls the directionality of a receiving beam.The receiving beam processing unit 682 then outputs the weightedreceived signal to the common digital unit 431.

4-3. Example of Signal Transmitting and Receiving Sequence

FIG. 21 is an explanatory view showing an example of a sequence ofsignals transmitted and received between the communication device 500and the communication device 600 described above. Referring to FIG. 21,signals transmitted from the communication device 500 (Tx) and thecommunication device 600 (Rx) are sequentially shown along the timeaxis.

First, the header portion of RTS conforming to the first communicationmethod is transmitted from the first radio communication unit 320 of thecommunication device 500. The header portion of RTS corresponds to theabove-described instruction signal. Next, subsequent to the headerportion of RTS, BTF conforming to the first communication method istransmitted from the first radio communication unit 320 of thecommunication device 500. The BTF corresponds to the above-describedbeam reference signal. An optimum transmitting beam pattern whentransmitting a signal from the communication device 500 to thecommunication device 600 is thereby determined in the first radiocommunication unit 620 of the communication device 600.

Next, CTS conforming to the first communication method is transmittedfrom the first radio communication unit 620 of the communication device600. The data portion of the CTS contains a parameter value thatspecifies an optimum transmitting beam pattern, for example. In thiscase, the CTS corresponds to the above-described notification signal. Ifit is assumed that the arrival direction of direct waves or reflectedwaves with the highest received power does not vary regardless of atransmission medium as described earlier, a result of learning with useof the BTF conforming to the first communication method can be appliedto radio communication in accordance with the second communicationmethod. Accordingly, the communication device 500 can be notified fromthe above-described CTS about the optimum transmitting beam pattern whentransmitting a signal to the communication device 600 in accordance withthe second communication method. Note that the CTS transmitted from thecommunication device 600 to the communication device 500 may also serveas the above-described instruction signal. In this case, the headerportion of CTS (i.e. the instruction signal) and BTF (i.e. the beamreference signal) are transmitted from the first radio communicationunit 620 of the communication device 600 to the communication device500.

After that, data is transmitted from the communication device 500 to thecommunication device 600 in accordance with the second communicationmethod, and ACK (acknowledgement) is transmitted back from thecommunication device 600 to the communication device 500. At this time,because the optimum transmitting beam pattern determined by learning isused between the communication device 500 and the communication device600, it is possible to transmit and receive data more reliably inaccordance with the second communication method even with use ofmillimeter waves with high straightness and short electric waveattainment distance.

4-4. Alternative Example

In this embodiment, the first digital unit 630 of the communicationdevice 600 may determine the direction where the communication device500 is located by using MUSIC (Multiple Signal Classification) method,which is known as a kind of eigenvalue analysis, for example. When usingthe MUSIC method, the first digital unit 630 of the communication device600 calculates a MUSIC spectrum depending on the direction where thecommunication device 500 is located based on the amplitude and phase ofthe received beam reference signal, for example. Next, the first digitalunit 630 estimates the direction in which the calculated value of theMUSIC spectrum is largest as the direction where the communicationdevice 500 is located. Then, the first digital unit 630 can determinethe optimum directionalities of transmitting and receiving beams whenperforming radio communication in accordance with the secondcommunication method according to the estimated direction.

5. Summary

The first to third embodiments of the present invention are describedabove with reference to FIGS. 1 to 21. In each embodiment, the receptionstart time point of the beam reference signal transmitted according tothe first or second communication method is determined based on theinstruction signal transmitted in accordance with the firstcommunication method. Reception of the beam reference signal is startedat the timing when the data portion omitted in the instruction signal isoriginally supposed to be received. Then, a parameter value forspecifying an optimum beam pattern is determined based on the beamreference signal. It is thereby possible to learn optimumdirectionalities of transmitting and receiving beams used for radiocommunication in accordance with the second communication method duringa time period in which one packet can be transmitted and received.Further, because a part of the circuit used for transmission andreception processing can be shared between the first and secondcommunication methods, it is possible to suppress an increase in circuitscale and reduce manufacturing costs or reduce the device size, as inthe second embodiment.

It should be noted that, although a configuration of a device at thetransmitting end and a configuration of a device at the receiving endare described separately for convenience of description, a communicationdevice which has both functions of the transmitting end and thereceiving end may be configured as a matter of course.

Further, in this specification, the case of determining a beam patternwith a maximum received power as an optimum beam pattern in a device atthe receiving end is described. Alternatively, however, a plurality ofbeam patterns with high received powers may be determined as candidatesof a beam pattern to be used. Radio communication using millimeter wavescan be thereby performed by the combined use of a plurality of beampatterns, for example.

Although preferred embodiments of the present invention are described indetail above with reference to the drawings, the present invention isnot limited thereto. It should be understood by those skilled in the artthat various modifications, combinations, sub-combinations andalterations may occur depending on design requirements and other factorsinsofar as they are within the scope of the appended claims or theequivalents thereof.

The present application contains subject matter related to thatdisclosed in Japanese Priority Patent Application JP 2009-032029 filedin the Japan Patent Office on Feb. 13, 2009, the entire content of whichis hereby incorporated by reference.

1-16. (canceled)
 17. An electronic device comprising: circuitryconfigured to: control transmitting an instruction signal to anotherelectronic device by a first frequency band, the instruction signalinstructing to learn a channel state information; and controltransmitting a reference signal to the another electronic device by asecond frequency band, the reference signal being for learning thechannel state information, wherein the second frequency band is higherthan the first frequency band.
 18. The electronic device of claim 17,wherein the channel state information is used to decide beamdirectionality.
 19. The electronic device of claim 18, wherein thecircuitry configured to control transmitting the reference signal aftera prescribed time period has elapsed from completion of transmission ofthe instruction signal.
 20. The electronic device of claim 18, whereinthe instruction signal contains only a header portion of a signal formattransmitted by the first frequency band.
 21. The electronic device ofclaim 18, wherein the reference signal is a signal containing pluralsignal sequences respectively associated with different directionalitypatterns.
 22. The electronic device of claim 21, wherein the referencesignal is a signal containing plural time slots respectivelycorresponding to the plural signal sequences.
 23. The electronic deviceof claim 21, wherein the reference signal is a signal combining theplural signal sequences in orthogonal or pseudo orthogonal relation withone another.
 24. The electronic device of claim 17, wherein at leastpart of transmission processing of a radio signal by the first frequencyband and at least part of transmission processing of a radio signal bythe second frequency band are executed using a common circuit.
 25. Theelectronic device of claim 17, wherein the instruction signal indicatesa reception start time of the reference signal.
 26. The electronicdevice of claim 17, further comprising: a plurality of antennasconfigured to receive the instruction signal and the reference signal.27. The electronic device of claim 26, wherein the plurality of antennasincludes at least one array antenna.
 28. The electronic device of claim26, wherein a number of the plurality of antennas is two.
 29. Theelectronic device of claim 26, wherein a number of the plurality ofantennas is more than three.
 30. The electronic device of claim 26,wherein the plurality of antennas includes a first antenna and a secondantenna, the first antenna is configured to transmit signals by thefirst frequency band and the second antenna is configured to transmitsignals by the second frequency band.
 31. An electronic devicecomprising: circuitry configured to: control receiving an instructionsignal to another electronic device by a first frequency band, theinstruction signal instructing to learn a channel state information; andcontrol receiving a reference signal to the another electronic device bya second frequency band, the reference signal being for learning thechannel state information, wherein the second frequency band is higherthan the first frequency band.
 32. The electronic device of claim 31,wherein the channel state information is used to decide beamdirectionality.
 33. The electronic device of claim 32, wherein thecircuitry configured to control receiving the reference signal after aprescribed time period has elapsed from completion of reception of theinstruction signal.
 34. The electronic device of claim 32, wherein theinstruction signal contains only a header portion of a signal formattransmitted by the first frequency band.
 35. The electronic device ofclaim 32, wherein the reference signal is a signal containing pluralsignal sequences respectively associated with different directionalitypatterns.
 36. The electronic device of claim 35, wherein the referencesignal is a signal containing plural time slots respectivelycorresponding to the plural signal sequences.
 37. The electronic deviceof claim 35, wherein the reference signal is a signal combining theplural signal sequences in orthogonal or pseudo orthogonal relation withone another.
 38. The electronic device of claim 31, wherein at leastpart of reception processing of a radio signal by the first frequencyband and at least part of reception processing of a radio signal by thesecond frequency band are executed using a common circuit.
 39. Theelectronic device of claim 31, wherein the instruction signal indicatesa reception start time of the reference signal.
 40. The electronicdevice of claim 31, further comprising: a plurality of antennasconfigured to receive the instruction signal and the reference signal.41. The electronic device of claim 40, wherein the plurality of antennasincludes at least one array antenna.
 42. The electronic device of claim40, wherein a number of the plurality of antennas is two.
 43. Theelectronic device of claim 40, wherein a number of the plurality ofantennas is more than three.
 44. The electronic device of claim 40,wherein the plurality of antennas includes a first antenna and a secondantenna, the first antenna is configured to transmit signals by thefirst frequency band and the second antenna is configured to transmitsignals by the second frequency band.
 45. A method comprising:transmitting, by a first frequency band, an instruction signalinstructing to learn a channel state information to another electronicdevice; and transmitting, by a second frequency band being higher thanthe first frequency band, a reference signal used for learning a channelstate information to the another communication device.
 46. The method ofclaim 45, wherein the instruction signal indicates a reception starttime of the reference signal.
 47. The method of claim 45, wherein thechannel state information is used to decide beam directionality.
 48. Amethod comprising: receiving, with a first radio communication unitcapable of radio communication in accordance with a first communicationmethod, an instruction signal instructing to learn a channel stateinformation from another communication device; and receiving, with asecond radio communication unit capable of radio communication inaccordance with a second communication method using a higher frequencyband than the first communication method, a reference signal used forlearning a channel state information from said another communicationdevice.
 49. The method according to claim 48, wherein the instructionsignal indicates a reception start time of the reference signal.
 50. Themethod according to claim 48, wherein the channel state information isused to decide beam directionality to said another communication device.